How to cull groups of MeshInstance together?

:information_source: Attention Topic was automatically imported from the old Question2Answer platform.
:bust_in_silhouette: Asked By Zylann
:warning: Old Version Published before Godot 3 was released.

I have a generated voxel world which contains a lot of MeshInstances in a 3D grid. Each MeshInstance is 16x16x16 in size and is recomputed every time a change is made to them.

I discovered that frustum culling was taking a lot of time, and increasing the step of the grid to 32x32x32 was better (8 times faster). However, I want to keep my meshes under 16x16x16 size because it’s cheaper to update them, as 32x32x32 would involve too much latency.

So my question is:
How can I make Godot cull groups of 2x2x2 MeshInstances together instead?